This invention will relate to a means for increasing the efficiency of high wattage amplifiers and will have specific application to a means for switching power supplies in large wattage amplifiers between a series and parallel arrangement for increased efficiency.
In industry, it is very often desirable to have an amplifier capable of producing a large amount of output power, generally in the range of several kilowatts. A good example of a situation where this power output is required would be in the field of AM radio where large amplifiers are used for transmitter modulators. Another common use of such large amplifiers is an excitor for vibration or shake tables used to test products against vibration. A problem associated with such large amplifiers is the generally poor efficiency of the amplifier which increases the operating and construction cost. A generally accepted definition of efficiency is the ratio of useful power delivered by a dynamic system to the power supplied to it. Industry has made several attempts to increase the efficiency of an amplifier. The most popular, however, is the pulse width modulation technique. In pulse width modulation, the amplitude of the signal to the amplifier remains constant with the pulse width varying. The advantage of pulse width modulation is that since the signal is of a constant amplitude the transistors used can function between cut off and saturation, thereby, increasing the efficiency of the amplifier by reducing the power dissipated in the system. To increase the efficiency of the amplifier further by reducing the amount of power that must be dissipated in the form of heat, it is typical to use a center tapped DC power supply with a complementary pair of pulse width modulated switches connected between the positive and negative voltage supplies and a load which is connected to the center tap. A problem associated with this is that in order to insure the maximum sharing and efficiency between the set of pulse width modulated switches, the components within the switches must be carefully and accurately selected and matched. If one switch is not speed matched to its complementary switch then a current will be generated which will pass through both switches and the efficiency of the system will drop.